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New P&W GTF Combustor-lining Design Will Aid Middle East Operations

 - October 29, 2017, 3:56 PM
With some of its geared turbofan (GTF) engines facing reliability issues in challenging operating environments, Pratt & Whitney responded with a new combustor-lining design.

Pratt & Whitney developed a new combustor-lining design as a result of lining-degradation issues experienced by airlines operating Airbus A320neos powered by PW1100G-JM geared-turbofan (GTF) engines in India’s high-particulate, low air-quality environment. The design will help ensure GTF engines also operate reliably in the Middle East, according to a knowledgeable source.

The engine-maker declined to comment on the specifics of any engine-reliability measures it is taking to ensure that its GTF engines operate reliably in the particulate dust-, sand- or salt-laden environments found in the Middle East, India and parts of China, but a source familiar with the component has detailed to AIN how P&W will boost GTF reliability in such environments.

According to the source, the PW1100G-JM’s new combustor-lining configuration has more cooling-air holes overall and a higher density of cooling holes in the combustor’s known hot spots than the previous design. So if some of a GTF engine’s air-cooling holes clog , the new combustor-lining design will provide more redundancy the amounts of cooling air being provided to the lining. This will give airlines better predictability for their scheduled operations of aircraft with GTF engines, the source said.

A Pratt & Whitney spokesperson has confirmed to AIN that some PW1500G engines powering Bombardier C series jets have also experienced combustor-lining degradation and oil leaks from the no. 3 bearing compartment carbon seal, like those that have affected many PW1100G-JMs powering the A320neo. However, the spokesperson said, because far fewer C Series jets are in service than are GTF-powered A320neos, there have been far fewer unscheduled PW1500G removals than those involving PW1100G-JMs. And P&W has delivered enough spare PW1500Gs to existing C Series operators to provide cover for any unscheduled removals that do happen.

P&W added that it will incorporate the new combustor design into all five existing members of the PW1000G engine family, along with the final fix P&W is developing to stop oil leaks from the no. 3 bearing compartment carbon seal.

Meanwhile, P&W made a strategic decision, in consultation with Airbus and Bombardier in late September, to allocate more current-production PW1000G engines as spares to the airline operators that experienced unscheduled removals of in-service GTFs. That has ended the aircraft-on-ground (AOG) difficulties the engine program had been facing, the manufacturer said.

P&W increased the number of MRO shops performing GTF overhauls from two to four and reduced GTF in-shop repair time to 45 from 60 days. Together with the manufacturer’s allocation of more new-production PW1100G-JMs and PW1500Gs as spares to A320neo-family and C Series operators, respectively, it reduced the global GTF-related AOG backlog to one aircraft by October 27. At one time 15 A320neos were grounded in India alone because of highly publicized technical issues affecting their PW1100G-JM engines’ combustor linings and no. 3 bearing compartment oil seals, the P&W spokesperson noted.

“We had a commitment to Airbus, and we had a commitment to Bombardier to deliver a certain number of engines this year to support their aircraft production plans…[but] we made the decision in early October or late September…that we were going to redirect a number of spares to our airline customers to make sure that they had enough assets to be able to fly their planes every day,” said Greg Hayes, CEO of P&W’s parent United Technologies, during the company’s 2017 third-quarter earnings conference call on October 24.

“While the GTF has a dispatch reliability of 99.8 percent, because of these two durability issues that we've been talking about, there were a number of aircraft that were on the ground for unacceptably long time periods,” Hayes said. “And so, working with Airbus, working with Bombardier, we agreed to take production engines and divert [them] into the spares fleet…we had to do what was right for the customer here…it was unfortunate that we couldn't meet our commitments to…Airbus and Bombardier, but they understood the need to keep the airline customers up flying, and we've done the right thing for the business in the long term.”

Along with P&W’s actions to clear the GTF-related backlog of grounded in-service aircraft worldwide, the company’s efforts to bolster its GTF fan-blade production capabilities—which represented a pacing item that created quality-control and volume-production issues for the GTF program for more than a year—are now over. P&W is confident it will meet its 350-400 GTF production target for 2017.

P&W’s major production-bottleneck problem with the GTF fan blades arose from the fact that originally only one facility—in Lansing, Michigan—was manufacturing the blades, which use an innovative aluminum-honeycomb structural design to make the blades extremely strong but also extremely light. Compounding the problem, only half of the shop’s early-production GTF fan blades were demonstrating the requisite design quality, and the rest had to be recycled.

Since then, however, the company has added two more facilities that are producing GTF fan blades, by opening another facility in Lansing and one in Japan, according to the P&W spokesperson. At the same time, P&W has overcome its initial blade manufacturing-quality issues, and 95 percent of the GTF fan-blades now being produced meet the required standards.

“The important thing is to look at the number of actual engines that we built in the [third] quarter, which is 120. And we're well on our way to hit that [targeted] 350 to 400 [this] year; probably almost doubling that again next year,” Hayes told financial analysts on October 24. Although Hayes declined to say how many of the 120 GTFs it delivered in the third quarter were sent to existing operators as spares and how many went to OEMs to install on new aircraft, the number of third-quarter deliveries “nearly matches” the entire number of GTF engines the company delivered in the first half of 2017, the P&W spokesperson said.

“Nothing is holding us back” any more, the spokesperson continued. “Now we’re just gearing up the mass of machinery on our way to peak maximum” annual production of PW1000Gs. “And as we make our way to the maximum peak, we continue to evolve the engine.”

According to the spokesperson, at maximum GTF production rates, each of the four final-assembly facilities producing the engines (in Middletown and West Palm Beach in the U.S., in Munich and Japan Aero Engine Company’s line at IHI in Mizuho) will be able to deliver 500 GTFs a year. There are two caveats to this statement: the number of engines delivered will depend on market demand for them (though P&W now has an order backlog of some 8,000 GTFs), and it is not clear yet if P&W’s supply-chain arrangements will allow each of the four assembly lines to deliver 500 engines a year in the same year. If conditions are suitable, however, P&W would then be delivering 2,000 GTF engines a year—almost as many units as CFM International envisions delivering at the planned maximum production rate for its LEAP engine family.

As for P&W evolving the GTF, the company recently completed more than 175 hours of ground-tests of second-generation GTF technology at its West Palm Beach engine test center under the FAA’s Continuous Lower Energy, Emissions and Noise (CLEEN) program. According to P&W, the engine—which was modified from an existing development example of the already-certified GTF family—operated successfully in a design space never before demonstrated, incorporating significantly fewer lower-pressure-ratio blades than current-production GTFs and a shorter duct inlet.

The company expects the engine testing, 275 hours of previous fan-rig tests and other forthcoming rig tests under the FAA’s follow-on CLEEN II program, to demonstrate a 2 percent fuel-burn improvement over the comparable existing GTF family member. By the mid-2020s, P&W expects to obtain another 3 to 5 percent fuel-burn improvement from further PW1000G-family technological development, which appears likely to include a new, advanced engine core for the family.